Jet Vermilion car
Go to the machine selection screen in grand prix mode. Press L, R, Start, R, L, Select to display the password screen. Go to the Nintendo Of Japan web site and enter your name exactly using the on-screen keyboard keys, then click on the "Confirm" button (furthest right). You will get a password which will allow you to get the top secret Jet Vermilion car. Enter that password in your game to unlock the car. There are also two other ways to unlock the Jet Vermilion car. One is to unlock all other cars and complete championship mode 255 times. The other is to complete every series on Master Class with all other racers.